The diversion of water from streams and rivers has been an integral part of the development of the industrial and agricultural economy of the Pacific Northwest and other regions. The diverted water has been used to generate hydropower to irrigate arid lands, for municipal water supplies and for industrial purposes, etc. Typically, the diversions are not screened, resulting in the ready movement of fish from the river into the diverted water flow and ultimately to their death. In the Pacific Northwest, unscreened water diversions, amongst other causes, have resulted in the extinction of steelhead and salmon from over 50% of their historic range and have critically reduced salmon populations in the rivers that salmon still inhabit. As a result, several species of Pacific Northwest salmon have gone extinct and several others are now listed as threatened or endangered.
During the development of irrigation and hydroelectric facilities, efforts have been made to achieve screened water diversion apparatuses that separate fish and/or debris from the diverted water flow. Generally speaking, these devices have not worked well and for that reason they are rarely used even though required by law in some instances. For example, in its 1996 study of Pacific Northwest salmon, the National Research Council reported that fewer than 1,000 of the 55,000 water diversions in Oregon alone were screened, and 3,240 were listed as a high priority for screening.
Representative fish screen embodiments are shown in U.S. Pat. Nos. 3,938,340 and 4,064,048, issued to Downs and U.S. Pat. No. 4,740,105, issued to Wollander. A common feature of these devices is that the fish screens are arranged substantially vertically. A significant problem with vertically arranged screens is that they are easily fouled or clogged, resulting in burdensome cleaning schedules or elaborate cleaning equipment that is of questionable efficacy (see, for example, the '105 patent).
Other screen arrangements are discussed in U.S. Pat. Nos. 4,526,494 and 5,385,428 issued to Eicher and Taft, respectively. These arrangements each employ a submerged diagonally disposed screen that slopes upwardly in the downstream direction. The diagonal screen promotes rapid movement of water through the screen and in principal generates a shear force that pushes smolt up the screen to a bypass mechanism. The rapid movement of water through the screen, however, causes debris and fish (particularly salmon smolt) to be driven into or accumulated at the screen, thus leading to fouling and fish loss. The screens of both the '494 and '428 patents are pivotally mounted for flushing this debris off the screens. In practice, the screens have also required additional cleaning and maintenance.
It should also be recognized that the devices of the '494 and '428 patents are for major hydroelectric installations which tend often to pass relatively high flow volumes and are much better capitalized than agricultural irrigation districts and the like. The devices of the '494 and '428 patents tend to be prohibitively expensive for low profit margin and non tax or rate payer supported installations such as agricultural fields and rural residential uses, etc.
It should also be recognized that the above-described screened water diversions do not approximate natural conditions, and thus they increase both physical stress on fish and fish mortality. For example, the '340 and '048 patents use a mechanical scoop that collects fish and drops them into a return conduit, while the '105 patent uses fish traps and a tubal transport system. Similarly, the '494 and '428 patents teach submerged conduits that use high velocity water flow through a tilted screen to shear fish off towards a bypass conduit. These are all unnatural stream features and work against advantageous natural flow dynamics.
A need thus exists for a screened water diversion that safely and efficaciously maintains fish in the non-diverted flow. A need also exists for such a screen diversion that approximates natural conditions, is substantially non-fouling and is low cost to implement and maintain. It should be recognized that such a screened water or fluid diversion, while suitable for fish passage, may also be used for other purposes.